98 BIRDS OF LA PLATA 
filling its crop with air, to use it as a “‘ chamber of 
resonance.” The note I have described is quickly 
and invariably followed by a scream, harsh and 
impetuous, uttered by the female, though both 
notes always sound as if proceeding from one bird. 
When on the wing the birds all scream together in 
concert. 
The food of this species is chiefly minute seeds 
and tender buds; they also swallow large cater- 
pillars and spiders, but do not, like their congeners, 
eat hard insects. 
I became familiar, even as a small boy, with the 
habits of the Screaming Cow-bird, and before this 
species was known to naturalists, but could never 
find its nest though I sought diligently for it. I could 
never see the birds collecting materials for a nest, 
or feeding their grown-up young like other species, 
and this might have made me suspect that they did 
not hatch their own eggs; but it never occurred to 
me that the bird was parasitical, I suppose because 
in summer they are always seen in pairs, the male 
and female being inseparable. Probably. this is the 
only parasitical species in which there is conjugal 
fidelity. I also noticed that when approached in the 
breeding-season the pair always displayed great 
excitement and anxiety, like birds that have a nest, 
or that have selected a site on which to build one. 
But year after year the end of the summer would 
arrive, the birds re-unite in parties of half a dozen, 
and the mystery remain unsolved. At length, after 
many years, fortune favoured me, and while ob- 
